This invention relates to liquid, storage-stable isocyanates prepared by reacting 4,4'-methylene bis(cyclohexyl-isocyanate) having a trans,trans-isomer content of from 35 to 100% by weight with a blocking agent.
4,4'-diisocyanato dicyclohexylmethane and the diamine precursor, 4,4'-diamino-dicyclohexylmethane, exist in three stereoisomeric forms (i.e. trans,trans; cis,trans; and cis,cis) as described, for example, in U.S. Pat. Nos. 2,606,925 and 3,789,032, Canadian Patents 961,049 and 971,184, and British Patent 1,220,715. Commercial grades of 4,4'-diamino-dicyclohexylmethane normally contain all three isomers.
U.S. Pat. No. 3,155,724 describes a process of producing 4,4'-diisocyanato dicyclohexylmethane from the amine precursor, wherein the resultant product has a trans,trans-isomer content of 54% and a melting point of about 58.degree. C. Accordingly, the 4,4'-diisocyanate dicyclohexylmethane is a semi-solid or slurry at room temperature.
In order for mixtures containing 4,4'-diisocyanato dicyclohexylmethane to be a liquid at room temperature, the content of the trans,trans-isomer must lie within a certain range. Liquid diisocyanate mixtures can be prepared by the phosgenation of 4,4'-diamino-dicyclohexylmethane (4,4'-HMDA), or its mixtures with the 2,4'- and/or 2,2'-HMDA isomers, wherein the content of the trans,trans-isomer of 4,4'-HMDA is less than about 25%. The trans,trans-isomer content of the diisocyanate corresponds to that of the amine precursor.
U.S. Pat. No. 5,175,350 discloses a process for the preparation of a 4,4'-diisocyanato dicyclohexylmethane which contains at least 90% by weight of the trans,trans-isomer. The process yields a liquid phase which contains from about 12 to about 25% by weight of the trans,trans-isomer, and a solid phase which contains at least about 90% by weight of the trans,trans-isomer.
U.S. Ser. No. 07/772,996, filed Oct. 8, 1991, describes a process for preparing free-flowing solids, which have many or the advantages of liquids, from 4,4'-diisocyanato dicyclohexylmethane having a trans,trans-isomer content of at least 90% by weight.
There are obvious advantages to a liquid diisocyanate compared to those that are fused solids or slurries at ambient temperature. A liquid is easier to pump and less expensive to transport. A liquid has a homogeneous composition as supplied without the need to homogenize it at elevated temperatures as is the case with slurries or fused solids. In the production of polyurethanes, a liquid can be added easily by weight or volume and combined with suitable coreactants at ambient temperatures. This is safer than using the materials at elevated temperatures due to the lower vapor pressure of the materials at room temperature.